检索所有数据然后过滤到表视图中的正确方法是什么？

Question

我正在成功检索 Firebase 数据并将其加载到我的 tableview 中。在初始加载时，我根据日期查询数据，因此它只加载日期在当前日期之后的数据。我还有一个“过去”按钮，它以相同的方式查询数据，但只显示日期早于当前日期的数据。它可以工作，但是我在每次单击按钮时都会检索数据，并且它似乎会降低性能并且有时会崩溃。这是这样做的方法吗？或者我可以通过什么方式加载所有数据和带有按钮的查询/过滤器？

override func viewDidLoad() {
    super.viewDidLoad()
//Retrieving data from Firebase
    refReleases = Database.database().reference().child("releases");
    _ = refReleases.queryOrdered(byChild: "date").queryStarting(atValue: currentDate).observe(.value, with: { (snapshot) in
        if snapshot.childrenCount>0{
            self.releasesData.removeAll()
          for releases in snapshot.children.allObjects as![DataSnapshot]{
                let releaseObject = releases.value as? [String: AnyObject]
                let releaseName = releaseObject?["releaseName"]
                let releaseType = releaseObject?["releaseType"]
                let releasePrice = releaseObject?["releasePrice"]
                let releaseDate = releaseObject?["releaseDate"]
                let releaseImage = releaseObject?["releaseImage"]
                let releasetag = releaseObject?["releasetag"]
                let releaseStyleCode = releaseObject?["releaseStyleCode"]
                let release = ReleaseModel(releasetype: releaseType as! String?, releasename: releaseName as! String?, releaseprice: releasePrice as! String?, releasedate: releaseDate as! String?, releaseimage: releaseImage as! String?, releasetag: releasetag as! String?, releasestylecode: releaseStyleCode as! String?) 
                self.releasesData.insert(release, at: 0)
            }
            self.releasesData.reverse()
            self.tableView.reloadData()
        }

    }
    )}
}

//"Past" button
@IBAction func past(_ sender: UIButton) {
    refReleases = Database.database().reference().child("releases");
    _ = refReleases.queryOrdered(byChild: "date").queryEnding(atValue: currentDate).observe(.value, with: { (snapshot) in
        if snapshot.childrenCount>0{
            self.releasesData.removeAll()
            for releases in snapshot.children.allObjects as![DataSnapshot]{
                let releaseObject = releases.value as? [String: AnyObject]
                let releaseName = releaseObject?["releaseName"]
                let releaseType = releaseObject?["releaseType"]
                let releasePrice = releaseObject?["releasePrice"]
                let releaseDate = releaseObject?["releaseDate"]
                let releaseImage = releaseObject?["releaseImage"]
                let releasetag = releaseObject?["releasetag"]
                let releaseStyleCode = releaseObject?["releaseStyleCode"]
                let release = ReleaseModel(releasetype: releaseType as! String?, releasename: releaseName as! String?, releaseprice: releasePrice as! String?, releasedate: releaseDate as! String?, releaseimage: releaseImage as! String?, releasetag: releasetag as! String?, releasestylecode: releaseStyleCode as! String?)
                self.releasesData.insert(release, at: 0)
            }
            self.tableView.reloadData()
        }

    }
    )}

Answer 1

您基本上每次单击“过去”按钮时都会添加观察者。 每次数据库中的值更改时，observe 方法都会触发。 另外，删除handle 是viewDidDisappear。

如果要手动读取一次数据，请使用observeSingleEvent 方法。 它只会触发一次。

另外，看看这个firebase blog post。 它显示了监听器的放置位置。

var handle: DatabaseHandle!

override func viewDidLoad() {
    super.viewDidLoad()
    //  Retrieving data from Firebase
    refReleases = Database.database().reference().child("releases")
}

override func viewWillApear(_ animated: Bool) {
    super.viewWillAppear(animated)
    handle = refReleases
        .queryOrdered(byChild: "date")
        .queryStarting(atValue: currentDate)
        .observe(.value) { snapshot in
            if snapshot.childrenCount > 0 {
                self.releasesData.removeAll()

                for releases in snapshot.children.allObjects as! [DataSnapshot] {
                    let releaseObject = releases.value as? [String: AnyObject]
                    let releaseName = releaseObject?["releaseName"]
                    let releaseType = releaseObject?["releaseType"]
                    let releasePrice = releaseObject?["releasePrice"]
                    let releaseDate = releaseObject?["releaseDate"]
                    let releaseImage = releaseObject?["releaseImage"]
                    let releasetag = releaseObject?["releasetag"]
                    let releaseStyleCode = releaseObject?["releaseStyleCode"]

                    let release = ReleaseModel(
                        releasetype: releaseType as! String?,
                        releasename: releaseName as! String?,
                        releaseprice: releasePrice as! String?,
                        releasedate: releaseDate as! String?,
                        releaseimage: releaseImage as! String?,
                        releasetag: releasetag as! String?,
                        releasestylecode: releaseStyleCode as! String?) 
                    self.releasesData.insert(release, at: 0)
                }
                self.releasesData.reverse()
                self.tableView.reloadData()
            }
        }
    }
}

override func viewDidDisappear(_ animated: Bool) {
    if let handle = handle {
        refReleases.removeObserver(withHandle: handle)
    }
}

Answer 2

但是我每次点击按钮时都会检索数据，而且速度似乎变慢了 性能有时会崩溃

因为你阻塞了主线程，你可以在Dispatch.main.async {}中做到这一点

Answer 3

李杰是对的。您不应该每次点击都添加观察者。您可以在过去的按钮中执行此操作，单击检查您的查询。如果存在，请将其删除。

        private var queryPast: Query?; // be sure firebase query. I do not remember. 
         override func viewDidLoad() 
        {
                super.viewDidLoad()
            //Retrieving data from Firebase
                refReleases = Database.database().reference().child("releases");
                _= refReleases.queryOrdered(byChild: "date").queryStarting(atValue: currentDate).observe(.value, with: { (snapshot) in
                    if snapshot.childrenCount>0{
                        self.releasesData.removeAll()
                      for releases in snapshot.children.allObjects as![DataSnapshot]{
                            let releaseObject = releases.value as? [String: AnyObject]
                            let releaseName = releaseObject?["releaseName"]
                            let releaseType = releaseObject?["releaseType"]
                            let releasePrice = releaseObject?["releasePrice"]
                            let releaseDate = releaseObject?["releaseDate"]
                            let releaseImage = releaseObject?["releaseImage"]
                            let releasetag = releaseObject?["releasetag"]
                            let releaseStyleCode = releaseObject?["releaseStyleCode"]
                            let release = ReleaseModel(releasetype: releaseType as! String?, releasename: releaseName as! String?, releaseprice: releasePrice as! String?, releasedate: releaseDate as! String?, releaseimage: releaseImage as! String?, releasetag: releasetag as! String?, releasestylecode: releaseStyleCode as! String?) 
                            self.releasesData.insert(release, at: 0)
                        }
                        self.releasesData.reverse()
                        self.tableView.reloadData()
                    }

                }
                )}
            }

            //"Past" button
            @IBAction func past(_ sender: UIButton) {
          if (self.queryPast != nil)
          {
             self.queryPast.removeObserver();
              // I DO NOT REMEMBER currently syntax. but you have  do something 
  like that.
          }
                refReleases = Database.database().reference().child("releases");
                self.queryPast = refReleases.queryOrdered(byChild: "date").queryEnding(atValue: currentDate);
       self.queryPast.observe(.value, with: { (snapshot) in
                    if snapshot.childrenCount>0{
                        self.releasesData.removeAll()
                        for releases in snapshot.children.allObjects as![DataSnapshot]{
                            let releaseObject = releases.value as? [String: AnyObject]
                            let releaseName = releaseObject?["releaseName"]
                            let releaseType = releaseObject?["releaseType"]
                            let releasePrice = releaseObject?["releasePrice"]
                            let releaseDate = releaseObject?["releaseDate"]
                            let releaseImage = releaseObject?["releaseImage"]
                            let releasetag = releaseObject?["releasetag"]
                            let releaseStyleCode = releaseObject?["releaseStyleCode"]
                            let release = ReleaseModel(releasetype: releaseType as! String?, releasename: releaseName as! String?, releaseprice: releasePrice as! String?, releasedate: releaseDate as! String?, releaseimage: releaseImage as! String?, releasetag: releasetag as! String?, releasestylecode: releaseStyleCode as! String?)
                            self.releasesData.insert(release, at: 0)
                        }
                        self.tableView.reloadData()
                    }

                }
                )}